The discovery in the Summer of 1988 of the Eurasian zebra mussel Dressiness polymorph in the Great Lakes of North America represents one of the most significant events in the history of aquatic biological invasion. However, this was not the first event of a non-indigenous species entering into US water. Earlier, the spiny water flea Bythotrephes cedarstroemi and the ruffe Gymnocephalus cernuus had entered the United States from ballast water of European ports. It was soon discovered that zebra mussel had also entered the US via ballast water of European origin.
Since the summer of 1988, there have been a number of aquatic species that have entered into the United States via ballast water taken from ports of other countries. It is estimated that several hundred organisms have been introduced into the US via ballast water and/or other mechanisms, not limited to fisheries and ocean or coastal currents. As such, the integrity of the coastal waters of the United States and the Great Lakes basin has been substantially threatened by the increased rate of aquatic species introduction from other countries.
Prior to 1880, various methods for controlling ballast in ships were used. In fact, many streets in coastal towns are paved with stones once used for ship ballast. However, shortly before the turn of the century, water as ballast soon replaced these older methods of stabilizing ships. The rate of invasions by non-indigenous aquatic species rose dramatically since the turn of the century, with much of this being attributed to shipping. As transoceanic travel increased, so to has the inadvertent introduction of non-indigenous species that threaten natural waterways. This is a result of the diverse array of organisms that are able to survive the transoceanic travel in ship ballast water, sea chests, and on ship hulls. Of these, the ballast water of ships is one of the primary mechanisms by which organisms have invaded US waters.
Ballast water consists of either fresh or salt water that is pumped into a vessel to help control its maneuverability as well as trim, stability, and buoyancy. The water used for ballast may be taken at various points during the voyage including the port of departure or destination. Container ships may make as many as 12 port visits/ballast exchanges during a single round-the-world journey. Any planktonic species or larvae that is near the ballast intake may be taken up and transported to the next port of destination. Globally, an estimated 10 billion tons of ballast water are transferred each year. Each ship may carry from a few hundred gallons (about 2 metric tons) to greater than 100,000 metric tons depending on the size and purpose. More than 640 tons of ballast water arrive in the coastal waters of the United States every hour.
The risk of invasion through ballast water has risen dramatically in the past 20 years as a result of larger vessels being used to transport greater amounts of material into and out of the U.S. It is estimated that between 3000-10,000 species of plants and animals are transported daily around the world. In regard to those materials being brought into the U.S., it is of interest to note that materials which contain animals, fruits, vegetables, etc., must be inspected by the United States Department of Agriculture in order to satisfy requirements that potentially harmful non-indigenous species are excluded. The irony is that the ship may be able to release ballast water that has been contaminated with a non-indigenous species. It is through this mechanism that several hundred species have been introduced into the United States.
The U.S. Fish and Wildlife Service currently estimates that the annual cost to the North American economy due to the introduction of non-indigenous species is more than $100 billion. While ballast water only accounts for a minor proportion of these introductions, the cost still runs to tens of billions of dollars in terms of industrial dislocation, clean-up, loss of product and loss of fisheries and other natural resources.
As noted above, one of the most notorious species introduced in the Great Lakes of North America is the Eurasian zebra mussel Dreissena polymorpha, which has become a major threat to inland water supplies from both a recreational and commercial aspect. Unfortunately, their range now extends from the Great Lakes to Louisiana and estimated economic losses are estimated at more than $4 billion for the calendar year 1999. This species is particularly prolific and a reproducing female can expel more than 40,000 fertile eggs per season which, upon hatching, may be found in colonies in excess of one hundred thousand per square meter. Furthermore, the colonies attach themselves to underwater structures that include, amongst others, water intake pipes, from which they can be readily disseminated into other environments, ship hulls, debris such as discarded automobile tires, sunken ships, and discarded metal drums. Established colonies often reach a thickness of 20 cm.
Of particular importance is the clogging of water intake pipes by zebra mussels that have a devastating industrial effect, especially in such uses as power plants, where there is a specific need for reliable water flow rates. Certain power plants have recorded a 50% water flow rate reduction following infestation and, in addition, zebra mussels appear to secrete substances, both in the living and dead state, that cause ferrous metal pipes to degrade. An associated problem also occurs in pipes that supply potable water because even following purification treatment, the water has an off flavor. This is attributed not only to the substances released by the living mussels, but especially by those that have died and are decaying. The latter most probably produce polyamines, such as cadaverine, which has a particularly obnoxious odor associated with decaying proteins and is most often noted in decaying meat.
Other detrimental environmental effects are the result of zebra mussel infestations both directly and indirectly. Of a direct nature are the effects on phytoplankton. Zebra mussels feed on phytoplankton, which are a source of food for fish, especially in lakes and ponds, thereby increasing the photosynthetic efficiency for other aquatic weed species because of increased clarity of the water. This has been shown to have dramatic effects on energy flow and food chains in some waters. Some fish species are threatened. The walleye, for example, thrives in cloudy water and it is generally believed by environmentalists that, increased water clarity resulted from zebra mussel activity will lead to the demise of that industry, presently estimated to be $900 million per year. Large-scale, multi-billion dollar degradations in native Great Lakes fisheries are already being felt as a result of competition from non-fishable species such as the Eurasian ruffe (Gymnocephalus cernuus) and the round goby (Proterorhinus marmoratus), which have been introduced through ballast water in the last two decades.
As a result of its feeding preferences, zebra mussels may radically alter the species composition of the algal community such that potentially harmful species may become abundant. An example is Microcystis, a blue-green alga of little nutritive value and capable of producing toxins which can cause gastrointestinal problems in humans. There are records of Microcystis blooms in Lake Erie and adjacent waterways. Toxic dinoflagellates such as Prorocentrum, Gymnodinium, Alexandrium and Gonyaulax often appear as blooms, sometimes known as “red tides”, in many parts of the world. Apart from causing serious (sometimes fatal) ailments in several vertebrate consumers, including humans, several of these organisms have had devastating effects on shellfish industries in several countries and it is now accepted that ballast-water introductions were responsible in many of these cases.
Reports of the introduction of the cholera bacterium, Vibrio cholera, to the Gulf coast of the United States have now been traced to the importation of this species associated with planktonic copepod (crustacean) vectors in ballast water arriving at Gulf coast ports from South America. This, in turn, had been transported from Europe to South American ports by similar means.
As a result of the introduction of non-indigenous species into the United States, and in order to reduce the possibility of the introduction of other organisms in the future, in 1990 the US Congress passed an act known as Public Law 101-646 “The Nonindigenous Aquatic Nuisance Prevention and Control Act” under the “National Ballast Water Control Program” which it mandates, among other things, studies in the control of the introduction of aquatic pests into the US. These control measures may include UV irradiation, filtration, altering water salinity, mechanical agitation, ultrasonic treatment, ozonation, thermal treatment, electrical treatment, oxygen deprivation, and chemical treatment as potential methods to control the introduction of aquatic pests. It is likely that other governments will pass similar legislation in the near future as the scope and costs of aquatic pest contamination become better understood.
Numerous methods and compositions have been proposed to control and inhibit the growth of various marine plants and animals. In particular, a number of compositions have been proposed to treat water and various surfaces having infestation of zebra mussels. Examples of various compositions are disclosed in U.S. Pat. Nos. 5,851,408, 5,160,047, 5,900,157 and 5,851,408. Treatment of various aquatic pests, other than toxic bacteria, is described in WO 00/56140 using juglone or analogs thereof.
These prior compositions and methods, although somewhat effective, have not been able to completely control the introduction of marine plants and animals into waterways. Accordingly there is a continuing need in the industry for the improved control of aquatic pests in the form of plants and animals, preferably aquatic flora, fauna, and other organisms that can be suspended in water and are susceptible to geographic migration by water intake, currents, or tides.